Here we go. There is nothing that can stir emotions among photographers like the debate as to which professional digital SLR is better - Canon or Nikon.
I started using Canon DSLRs back in 2002. I plunked down $5000 for a 4 megapixel Canon 1D. It was worth every penny. It was fast, rugged, great autofocus and the picture quality was outstanding (relatively speaking for 2002). The Canon lenses were all top notch. I bought the 16-35mm, 24-70mm, 70-200mm, 200mm F1.8 (what a great piece of glass), 85mm F1.2, 100mm F2.0, 50mm F1.4, and the 24mm F1.4. All great lenses and combined with the 1D bodies they really created some great photos with the help of the photographer.
I bought the Canon 1DS, the Canon 1D Mark II, the Canon 1DS Mark II, and the Canon 1D Mark III. These were all great cameras for their time and Canon was the clear leader over Nikon for low noise, high ISO images and they were the only manufacture with a full frame 35mm camera with the 1DS models.
Nikon had the 1.5 cropped sensor, and their high ISO performance was always a step behind Canon.
In 2007 everything changed. Nikon introduced the 12 megapixel, full frame, high ISO (low noise up to 6400 ISO), rugged, great autofocus Nikon D3.
During this time Canon introduced the Canon 1DS Mark III which took the pixel count over 21mp and only slightly improved the high ISO capabilities of the Canon 1DS Mark II. The Canon 1D Mark III was a great camera ... 10mp, 1.3 cropped senor with respectable high ISO up to 3200. Many users reported autofocus problems with the Canon 1D Mark III, but I never really experienced that. Many Canon users started using the Canon 5D ... a full frame 13mp camera in a pro-sumer body. The problem with the 5D was its autofocus system. It was basically the same system as found in the consumer level Canon 40D model. The focus points were tightly bunched in the middle of the finder and they weren't as sensitive or accurate as their Canon 1D big brother, leading to a lot of out of focus shots. In good light this camera produced great images, but if you were photograping moving subjects in poor light you were in trouble. Canon then came out with the 5D Mark II which took the pixel count over 21mp and improved the high ISO performance, but the autofocus system was still pro-sumer and the 21mp was overkill for what I needed.
As a photojournalist and wedding photographer 12mp is the sweet spot for resolution. The images are big enough to allow you to enlarge photographs up to 24 x 36, yet small enough as not to fill up CF cards and hard drives quickly and take longer to process on my Mac.
I bought the Nikon D3 for $5000 in 2007 to replace my Canon 1DS Mark II. The Canon 1DS Mark III was $8000 and 21mp (overkill for me) and the ISO performance was two stops worse than the D3. Then I bought the Nikon 14-24 and the Nikon 24-70 lenses. Both lenses were newly introduced and were amazingly sharp.
I used the Nikon D3 along side the Canon 1D Mark III for about 6 months. When Nikon introduced the Nikon D700 in the summer of 2008 I made the switch to Nikon 100%. I bought the 70-200mm F2.8, 50mm F1.4, 85mm F1.4, and the 16mm fisheye to go along with my other 14-24mm and my 24-70mm lenses. The D700 was about $2,700 and had the same exact full frame image senor and autofocus system as in the D3 in a slightly smaller and lighter body.
I also bought a few Nikon SB800 flashes and later the SB900 flash. I have no hard core testing on this, but the Nikon flashes seem to be more accurate and the iTTL system seems to work much better and easier than the Canon wireless flash system.
After I switched to the Nikon system the number of keepers for a wedding went up by 25%. My in-focus and properly exposed shots were much higher with the Nikon. Maybe I became a much better photographer, but it seems like quite a coincidence.
Come forward to 2010 ... Canon has introduced its 15mp, 1.3 cropped sensor 1D Mark IV with better high ISO, but still a stop or so worse than the new full frame, 12mp, Nikon D3s that was introduced in late 2009. Canon doesn't seem to get it. Give your customers better ISO and a full frame camera, and stop trying to cram more pixels into a cropped sensor.
Nikon has introduced a new 70-200mm F2.8 that is just amazing. I shoot it wide open and it produces wonderfully sharp images. Canon also introduced a new 70-200 that I am sure is also excellent.
In terms of lenses, both Nikon and Canon have a great lineup ... you won't go Canon or Nikon because of the lenses.
If you doing landscapes or in-studio portraits, you can't go wrong with either system. If your on the go and working in low light conditions, Nikon, IMO, gives you the best option.
I just bought a new Nikon D3S from Amazon. The D3S is very hard to find. B&H and Adorama were sold out. I received it on Wednesday and I photographed two weddings with it two days later.
I have been using the Nikon D3 for over three years and the Nikon D700 for over two years. The D3S looks and handles almost identically to the Nikon D3. I photographed two weddings this past week with the D3 and D3S. Some people have said they think the D3S focuses faster than the D3. It is my understanding that the autofocus technology is the same in both cameras. I didn't notice any real difference. Given that the D3 focuses great in even low light, that is not bad.
The D3 is a great low light / low noise camera and I wouid shoot at 6400 ISO at receptions or ceremonies when the light was low and flash wasn't a good option. The Nikon D3S just adds to the low light goodness of the D3. Nikon was smart and DID NOT add more megapixels to the sensor. Unlike Canon who is still in love with more and more megapixles, Nikon understands that 12 megapixels on a full frame sensor is what the professional photographer wants and needs when shooting action and low light situations like weddings, news, and sports.